Pressure test device for an inflator housing

ABSTRACT

A pressure test device for testing a heat resistance of an inflator housing is disclosed. The inflator housing is made from metal into a generally cylindrical contour and is filled with a gas. The test device includes a heating apparatus for heating the inflator housing. The heating apparatus includes a conducting wire, a heating coil that is connected with the conducting wire and causes induction heating in the inflator housing as set at a heating position, and a power supply that feeds a high-frequency electric current to the conducting wire.

CROSS REFERENCE TO RELATED APPLICATIONS

The Present application claims priority from Japanese Patent ApplicationNo. 2017-229664 of Makino et al., filed on Nov. 29, 2017, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a pressure test device for a housing ofan inflator which is used in an airbag device for a vehicle.

2. Description of Related Art

Conventionally, an inflator for use in an airbag device is formed byinserting such a gas as a nitrogen gas, in a pressurized form, in agenerally cylindrical housing made from such high strength metal asiron. When fed with an actuating signal, a squib and/or a micro gasgenerator disposed inside the inflator housing is ignited, whichinitiates burning of propellant. The burnt propellant generates gases,the gasses pressurize the housing, and a burst disc that has partitionedthe housing breaks, then the pressurized gases are discharged from gasdischarge ports formed in a leading end region of the housing, therebyinflating an airbag.

Pressure resistance of an inflator housing is very important for asecure deployment of the airbag because a problem in pressure resistancemay cause a gas leakage. Thus inflator housings are subjected topressure test prior to use. JP 2003-35643 A discloses a pressure testdevice for an inflator housing. The device tests pressure resistance ofan inflator housing by injecting water into the housing and checkingwhether water leakage occurs or not.

Other types of pressure test device includes one that conducts a test byplacing an inflator housing filled with gases (i.e. pressurized gases)in an electric furnace, heating the housing in the furnace and checkingwhether gas leakage occurs or not.

However, the testing using water requires removal of the water after thetesting, which complicates the testing. The testing using an electricfurnace requires a lot of time and a great deal of energy for heatingthe air in the furnace in order to heat and pressurize the inflatorhousing.

SUMMARY OF THE INVENTION

The invention contemplates a solution to the above-mentioned problems,and has an object to provide a pressure test device for an inflatorhousing which is capable of conducting a pressure test easily andquickly with less energy.

The object of the invention will be achieved by a following pressuretest device for an inflator housing:

The pressure test device for testing a heat resistance of an inflatorhousing includes a heating apparatus that heats the inflator housingwhich is made from metal into a generally cylindrical contour and isfilled with a gas. The heating apparatus includes a conducting wire, aheating coil that is connected with the conducting wire and causesinduction heating in the inflator housing as set at a heating position,and a power supply that feeds a high-frequency electric current to theconducting wire.

With the pressure test device of the invention, since the heatingapparatus heats the inflator housing directly by means of inductionheating, the inflator housing is heated more quickly for a pressure testthan in a conventional way of testing with the use of an electricfurnace. Further, the pressure test device of the invention uses lessenergy than the electric furnace in order to heat the inflator housingto a predetermined temperature. Further, the pressure test device of theinvention is able to conduct a pressure test merely by heating aninflator housing filled with a gas, thus is able to conduct the testmore easily than another conventional way of testing with the use ofwater.

Therefore, the pressure test device of the invention is conducive to aneasier, quicker and more energy-saving pressure test of an inflatorhousing.

If the inflator housing as subjected to the pressure test is judged tohave a sufficient pressure resistance (i.e. if the housing has no traceof gas leakage), it can be used as an inflator. To the contrary, if theinflator housing as ejected from the pressure test device shows a traceof gas leakage, it is unadapted for use as an inflator.

In the pressure test device of the invention, it is desired that theheating coil for causing induction heating is disposed at a position ina direction perpendicular to an axial direction of the inflator housingas set at the heating position.

With this configuration, since the inflator housing is generallycylindrical in outer contour and the heating coil is disposed at aposition in the direction perpendicular to the axial direction of theinflator housing as set at the heating position, induction heatingoccurs generally uniformly in a generally entire area in the axialdirection of the housing, thus heating the housing quickly.

In the above instance, it is further desired that the heating coilincludes a void space that serves as an insert/eject port of theinflator housing into and out of the heating position, and that theheating coil is configured to cover a portion of an outer circumferenceof the inflator housing opposed to the void space over a generallyentire length.

This configuration enables a setting and an ejection of the inflatorhousing as held by a suitable holding member, by way of example, in andout of the heating position to be conducted via the void space. Since noconducting wire is disposed in the void space, the setting and ejectionof the inflator housing can be conducted easily with no fear ofinterference by the conducting wire, which will be conducive to aspeed-up of the pressure test.

In this instance, it is desired that the heating coil is formed intosuch a bent plate shaped generally like a half-pipe that is adapted toencircle the portion of the outer circumference of the inflator housingopposed to the void space.

With this configuration, the heating coil encircles the outercircumference of the inflator housing in proximity over a generallyentire length of the inflator housing as set at the heating position atan opposite side of the void space. This will improve an efficiency ininduction heating of the inflator housing, thus contributing toenergy-saving in the pressure test.

In the instance where the heating coil is formed into the bent plate asdescribed above, it is desired that a projected contour of the heatingcoil as viewed from the axial direction of the inflator housing as setat the heating position is such a U shape that includes a semicirculararc portion which is opposed to the void space and covers a generallyhalf circumference of the inflator housing and a pair of straightportions that extend straightly in parallel to each other from both endsof the semicircular arc portion, and that at least leading ends of thestraight portions extend to a vicinity of a top of a portion of theouter circumference of the inflator housing disposed towards the voidspace.

With this configuration, when the inflator housing is disposed at theheating position, the semicircular arc portion of the heating coilencircles the generally half outer circumference of the housing inproximity at the opposite side of the void space and the straightportions sandwich the opposite portion of the outer circumference of theinflator housing in proximity though not in an encircling manner, thusthe heating coil encircles a generally entire outer circumference of theinflator housing over the entire length except a portion facing the voidspace. Therefore, the heating coil is able to heat the inflator housingefficiently by induction heating. Needless to say, the void space has anopening width greater than a diameter of the inflator housing and isdisposed at a position in the direction perpendicular to the axialdirection of the inflator housing as set at the heating position,thereby facilitating setting and ejection of the inflator housing in andout of the heating position by the heating coil.

Furthermore, in the instance where the heating coil includes the voidspace as described above, the void space is desirably disposed at alower portion of the heating coil such that the heating coil receivesthe inflator housing as laid horizontally from below the void space.

With this configuration, if the inflator housing as laid horizontally ismoved upward into the heating coil via the void space, the inflatorhousing is set at the heating position proximate to the heating coil.With this configuration, furthermore, since the setting of the inflatorhousing at the heating position can be conducted merely by moving thehousing upward, a holding member for holding the inflator housing hasonly to support an underside of the housing, i.e. does not have to becomposed of a chucking mechanism or the like that grips the inflatorhousing. By way of example, the holding member will have only toinclude, on the top plane, a V-shaped or U-shaped holding recess thataccommodates the inflator housing and prevents the same from slipping orrotating. Furthermore, although a chucking mechanism or the like wouldbe likely to be formed of metal material, such a holding member thatreceives the inflator housing in the V-shaped groove or the like may befabricated of non-conducting material like synthetic resin. That way thepressure test device will have only to heat the inflator housing but notthe holding member, and heating of the inflator housing will beconducted further efficiently.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view of an inflator composed of aninflator housing which is to be subjected to a pressure test with apressure test device embodying the invention;

FIG. 2 illustrates a production process of the inflator of FIG. 1schematically;

FIG. 3 is a schematic vertical sectional view of the pressure testdevice embodying the invention, taken along a direction perpendicular toan axial direction of the inflator housing;

FIG. 4 is a schematic vertical sectional view of the pressure testdevice of FIG. 3 taken along the axial direction of the inflatorhousing;

FIG. 5A is a plan view of a heating coil for use in the pressure testdevice as developed flatly;

FIG. 5B is a plan view of the heating coil as formed into a generallyhalf-pipe contour;

FIG. 5C is a front elevation of the heating coil of FIG. 5B; and

FIG. 6 is a schematic perspective view of the heating coil of FIG. 5B.

DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are described below withreference to the accompanying drawings. However, the invention is notlimited to the embodiments disclosed herein. All modifications withinthe appended claims and equivalents relative thereto are intended to beencompassed in the scope of the claims.

Firstly, an inflator 1 is described referring to FIGS. 1 and 2. Theinflator 1 is formed including an inflator housing 2 which is to besubjected to a pressure test conducted with a pressure test deviceembodying the invention. The inflator 1 is a hybrid inflator whichutilizes a combustion gas generated by burning of propellant and apressurized gas G of nitrogen, argon or the like inserted in the housing2 both for inflating an airbag. The housing 2 of the inflator 1 isgenerally cylindrical in outer contour, and includes a generallycylindrical body 4 having a constricted rear end, a discharging-side endcap 8 which is secured to the front end of the body 4 by welding or thelike, and a squib-side end cap 11 which is secured to the rear end ofthe body 4 by welding or the like. The body 4 is composed of a hollowpipe. The discharging-side end cap 8 is provided with a head 8 a havinga plurality of gas discharging ports 8 b. The squib-side end cap 11stores there inside a quantity of propellant 15 and a squib 14 forigniting the propellant 15.

One each burst disc 9, 12 is disposed to seal the body 4 at a boundarybetween the body 4 and discharge-side end cap 8 and at a boundarybetween the body 4 and the squib-side end cap 11. Each of the burstdiscs 9 and 12 is rupturable when impacted by an impact wave generatedby ignition of the squib 14 or pressure elevation due to burning of thepropellant 15. The body 4 between the burst discs 9 and 12 is filledwith the gas G under pressure of approximately between 35 and 70 MPa.When the inflator 1 is actuated, the squib 14 is ignited and burns thepropellant 15. The burnt propellant 15 generates combustion gases, thegases break the burst disc 12, then when an internal pressure of thebody 4 soars, the burst disc 9 breaks, thus the combustion gases of thepropellant 15 and the pressurized gas G are discharged from the gasdischarge ports 8 b.

The body 4 and end caps 8 and 11 of the inflator housing 2 are formedfrom pressure-resistant metal material such as low-carbon steel orsteel, which are conductor. The body 4 is provided, at a generallycenter in the front and rear direction, with an insert opening 5 fromwhich the pressurized gas G is inserted. The insert opening 5 is stoppedup by a stopper plug 6. The stopper plug 6 is formed from such metalmaterial that can be used for resistance welding, such as low-carbonsteel. The stopper plug 6 is welded to a periphery of the insert opening5 by resistance welding.

Production of the inflator 1 is now described. Firstly, the body 4 andthe end caps 8 and 11 to which the burst discs 9 and 12 have beenattached in advance, are provided. As shown in (A) of FIG. 2, the endcaps 8 and 11 are welded to the opposite ends of the body 4 to form thehousing 2. Then a pressurized gas G is inserted into the body 4 from theinsert opening 5 as shown in (B) of FIG. 2, then the stopper plug 6 isput into the insert opening 5, and welded to the periphery of theopening 5. The inflator 1 or inflator housing 2 thus produced issubjected to a pressure test using a pressure test device 20 shown inFIGS. 3 and 4 in order to check whether the inflator 1 has an enoughpressure resistance not to cause gas leakage. If the test result showsthat the inflator 1 has an enough pressure resistance not to cause gasleakage, the propellant 15 is inserted into the squib-side end cap 11and the squib 14 is secured to the squib-side end cap 11 as shown in (C)of FIG. 2. Thus the inflator 1 is completed.

As can be seen in FIGS. 3 and 4, the pressure test device 20 includes aninduction heating apparatus 40, a holding member 26 that holds andtransfers the inflator housing 2, and a cover 21 that covers theinflator housing 2 disposed at a heating position HP.

The cover 21 is fabricated of high strength metal such as iron, andincludes a ceiling wall section 22, a side wall section 23 which extendsdownwardly from an outer circumferential edge of the ceiling wallsection 22 in the form of a generally square tube, and a gateway 24which is disposed at a lower region of the side wall section 23, apartfrom the ceiling wall section 22. The heating position HP of theinflator housing 2 is disposed proximate to and beneath the ceiling wallsection 22. The housing 2 held by the holding member 26 is transferredupwardly to the heating position HP inside the cover 21 from a waitingposition WP outside of the cover 21 via the gateway 24.

The holding member 26 includes one or more holding sections 27 that holdthe housing 2, and is connected to a not-shown transfer mechanism. Inthe illustrated embodiment, the holding member 26 is configured to holdthe housing 2 in such a manner that the axial direction XD of thehousing 2 extends along a horizontal direction HD. The transfermechanism is configured to move the holding member 26 as holding thehousing 2 in an up and down direction as well as in the horizontaldirection. More specifically, as can be seen in FIG. 3, the not-showntransfer mechanism is capable of moving the inflator housing 2reciprocally from the waiting position WP disposed immediately below thegateway 4 of the cover 21 to a preparation position PP or to an ejectionposition EP disposed to a side in the horizontal direction HD, and fromthe waiting position WP to the heating position HP in the up and downdirection VD. The transfer mechanism may be configured to conducttransfer of the housing 2 manually, or may be connected to a powersupply 41 of the induction heating apparatus 40 so as to cooperate withthe induction heating apparatus 40 and move the housing 2 automaticallyfrom the preparation position PP to the waiting position WP, heatingposition HP, then waiting position WP again and to the ejection positionEP in parallel to a process of the pressure test.

Each of the holding sections 27 (27A, 27B) is formed into a plate whichis provided with a holding recess 29 for receiving the inflator housing2 on the top plane 28. In the illustrated embodiment, two of the holdingsections 27 are provided at two spaced-apart positions in the axialdirection XD so as to support an outer circumferential plane 3 of thehousing 2 (i.e. of the body 4). In the illustrated embodiment, theholding recess 29 of each of the holding sections 27 is composed of aV-groove 30 which dents downwardly and includes a bottom 30 a and a pairof flat supporting planes 31 and 32 extending upwardly from the bottom30 a in a V-shape. The holding sections 27 are each configured tosupport the outer circumferential plane 3 of the housing 2 as laid suchthat the axial direction XD extends along the horizontal direction HD,with the supporting planes 31 and 32. More particularly, the supportingplanes 31 and 32 support portions 3 h of a lower portion 3 b of theouter circumferential plane 3 of the housing 2, which portions 3 h aredisposed on both sides of a top 3 e of the lower portion 3 b whichprotrudes most downwardly.

The holding member 26 is fabricated of heat-resistant synthetic resin,i.e. non-conducting material, including the holding sections 27.

The induction heating apparatus 40 includes a conducting wire 43, whichis provided with an inductor or heating coil 46, and a power supply 41that feeds a high-frequency electric current to the conducting wire 43.

The power supply 41 includes an inverter circuit and one or moreoperating switches, and feeds a high-frequency electric current to theconducting wire 43 through the use of a commercial power. The powersupply 41 is configured to feed the current to the conducting wire 43when the housing 2 is placed at the heating position HP, and isconfigured to stop the supply of current when the housing 2 is heated toa predetermined temperature required for the pressure test.

The conducting wire 43 includes lead wires 44 and 45 extending from thepower supply 41 and the heating coil (inductor) 46 which is connected tothe leading ends of the lead wires 44 and 45 so as to generate eddycurrents in the housing 2 and induce heating of the housing 2. Theheating coil 46 is arranged in a spiral pattern.

As can be seen in FIG. 5A, the heating coil 46 as flatly developed has arectangular spiral contour that includes long sides 47 (47A and 47B)which are opposed to each other and short sides 48 (48A and 48B) whichare opposed to each other. More particularly, starting the lead wire 44at the center of the spiral, by way of example, the heating coil 46extends outwardly forming rectangular frames with a long side 47A1, ashort side 48A1, a long side 47B1, a short side 48B1, a long side 47A2,a short side 48A2, a long side 47B2, a short side 48B2, a long side47A3, a short side 48A3, a long side 47B3, a short side 48B3, a longside 47A4, a short side 48A4, a long side 47B4, a short side 48B4, andleads to an extended region 45 a of the lead wire 45 which is disposedproximate to the lead wire 44 disposed at the center of the spiral.

The long side 47 has such a dimension that covers a generally entirelength of the housing 2, and the short side 48 has such a dimension thatcovers the outer circumferential plane 3 of the housing 2 generallyentirely.

The heating coil 46 is disposed immediately below the ceiling wallsection 22 of the cover 21 in a direction YD perpendicular to the axialdirection XD of the housing 2 as positioned at the heating position HPso as to cause induction heating in the housing 2 positioned at theheating position HP. The heating coil 46 has a void space 53 that servesas an insert/eject port of the housing 2 into and out of the heatingposition HP, and encircles a portion of the outer circumferential plane3 of the housing 2 opposed to the void space 53 over a generally entirelength. In the illustrated embodiment, the heating coil 46 is formedinto such a bent plate shaped like a half-pipe that is capable ofcovering the portion of the outer circumferential plane 3 of the housing2 opposed to the void space 53 over the generally entire length, i.e.the upper portion 3 a of the outer circumferential plane 3.

Such a shape of the heating coil 46 can be formed by bending the shortsides 48 (48A, 48B) of the heating coil 46 as flatly developed as can beseen in FIG. 5A such that opposite ends 48 b and 48 c of each of theshort sides 48A and 48B are disposed farther downward than the center 48a as shown in FIG. 5C.

Moreover, as can be seen in FIGS. 3, 5B and 6, a projected contour ofthe heating coil 46 of the illustrated embodiment as viewed from theaxial direction XD of the housing 2 as set in the heating position HP issuch a U shape (more particularly, an inverse U shape) that includes asemicircular arc portion 49 that is opposed to the void space 53 andcovers a generally half circumference of the housing 2 and a pair ofstraight portions 50 and 51 that extend straightly downward in parallelto each other from both ends 49 a and 49 b of the semicircular arcportion 49. At least the leading ends 50 a and 51 a of the straightportions 50 and 51 extend to a vicinity of the top 3 e of the lowerportion (i.e. the portion disposed towards the void space 53) 3 b of theouter circumferential plane 3.

How an inflator housing 2 filled with a pressurized gas G is subjectedto a pressure test using the pressure test device 20 described above isnow described. As can be seen in FIG. 3, the not-shown transfermechanism firstly transfers the housing 2 from the preparation positionPP to the waiting position WP, then to the heating position HP. When thepower supply 41 of the induction heating apparatus 40 is turned on, theheating coil 46 generates magnetic field lines, such that eddy currentsare generated in the housing 2 and the housing 2 is heated to apredetermined temperature. Then the power supply 41 is turned off and,the housing 2 is transferred from the heating position HP to the waitingposition WP, then to the ejection position EP. The ejected housing 2 issubjected to judgment as to whether it is leaking gases or whether ithas a trace of gas leakage. The pressure test is thus completed.

Since the heating apparatus heats the housing 2 directly by means ofinduction heating, the pressure test device 20 of the illustratedembodiment is able to heat the inflator housing 2 more quickly for apressure test than a conventional way of testing with the use of anelectric furnace. Further, the pressure test device 20 of theillustrated embodiment uses less energy than the electric furnace inorder to heat the housing 2 to a predetermined temperature.Specifically, the pressure test device 20 spent approximately only onefifth of the electricity that the conventional electric furnace requiredfor the test. Moreover, the pressure test device 20 is able to conduct apressure test merely by heating an inflator housing 2 filled with a gas(pressurized gas) G, thus is able to conduct the test more easily thananother conventional way of testing with the use of water.

Therefore, the pressure test device 20 of the illustrated embodiment isconducive to an easier, quicker and more energy-saving pressure test ofthe housing 2 of the inflator 1.

If the inflator housing 2 as subjected to the pressure test is judged tohave a sufficient pressure resistance (i.e. if the housing 2 has notrace of gas leakage due to breakage of a burst disc 9, 12 or due todeficient welding), the housing 2 can be used as the inflator 1. Such ahousing 2 is filled with propellant 15 and assembled with the squib 14as shown in (C) of FIG. 2 to produce the inflator 1. To the contrary, ifthe housing 2 as ejected from the pressure test device 20 shows a traceof gas leakage, it is unadapted for use as the inflator 1, thus isdiscarded.

In the pressure test device 20 of the illustrated embodiment, theheating coil 46 for causing induction heating is disposed at a positionin the direction YD perpendicular to the axial direction XD of theinflator housing 2 as set at the heating position HP.

With this configuration, since the inflator housing 2 is generallycylindrical in outer contour and the heating coil 46 is disposed at aposition in the direction YD perpendicular to the axial direction XD ofthe inflator housing 2 as set at the heating position HP, inductionheating occurs generally uniformly in a generally entire area in theaxial direction XD of the housing 2, thus heating the housing 2 quickly.

The heating coil 46 of the foregoing embodiment is configured toencircle a generally half circumference of the housing 2 as set at theheating position HP. Alternatively, in order that the induction heatingcoil 46 is disposed at a position in the direction YD perpendicular tothe axial direction XD of the inflator housing 2 as set at the heatingposition HP, it is conceivable to form the heating coil 46 into a flatplate as can be seen in FIG. 5A and locate the same generallyimmediately beneath the ceiling wall section 22 of the cover 21. Furtheralternatively, the heating coil 46 may be formed into such a helicaltube or hose that has an inner diameter great enough to accommodate theinflator housing 2 such that the housing 2 may be inserted into the coil46 as formed into a tube and heated there, at the heating position HP.In either instance of the above alternative configurations, the housing2 will be heated generally uniformly over the entire length by inductionheating when the heating coil 46 is fed with a high-frequency electriccurrent.

In the pressure test device 20 of the illustrated embodiment, theinduction heating coil 46 is configured to include the void space 53that extends over a generally entire length of the housing 2, and isconfigured to encircle the upper portion 3 a of the outer circumference3 of the inflator housing 2 opposed to the void space 53 over thegenerally entire length. This configuration enables a setting of thehousing 2 at the heating position HP and an ejection of the housing 2out of the heating position HP to be conducted via the void space 53like in the illustrated embodiment, in which the housing 2 held by theholding member 26 and placed on the waiting position WP is moved upwardand set at the heating position HP via the void space 53, and thenejected back to the waiting position WP via the void space 53. Since noconducting wire 43 is disposed in the void space 53, the setting andejection of the housing 2 can be conducted easily with no fear ofinterference by the conducting wire 43, which will be conducive to aspeed-up of the pressure test.

In the pressure test device 20 of the illustrated embodiment, theheating coil 46 is formed into such a bent plate shaped generally like ahalf-pipe that is adapted to encircle the upper portion 3 a of the outercircumference 3 of the inflator housing 2 (i.e. the portion 3 a of theouter circumference 3 opposed to the void space 53).

With this configuration, the heating coil 46 encircles the upper portion3 a of the outer circumference 3 of the inflator housing 2 (i.e. theportion 3 a of the outer circumference 3 opposed to the void space 53)in proximity over a generally entire length of the housing 2 as set atthe heating position HP. This will improve an efficiency in inductionheating of the housing 2, thus contributing to energy-saving in thepressure test.

If such an advantageous effect does not have to be considered, theheating coil 46 may be formed into a flat spiral instead of a bent plateas illustrated in FIG. 5A and disposed immediately beneath the ceilingwall section 22 of the cover 21, Such a configuration will yet form agreat void space 53 continuous with the gateway 24 below the coil, andfacilitate a setting and an ejection of the housing 2 in and out of theheating position HP.

In the illustrated embodiment, moreover, the projected contour of theheating coil 46 as viewed from the axial direction XD of the inflatorhousing 2 as set at the heating position HP is such a U shape(particularly, an inverse U shape) that includes the semicircular arcportion 49 which is opposed to the void space 53 and covers a generallyhalf circumference 3 a of the inflator housing 2 and a pair of thestraight portions 50 and 51 that extend straightly in parallel to eachother from both ends 49 a and 49 b of the semicircular arc portion 49.The leading ends 50 a and 51 a of the straight portions 50 and 51 extendto a vicinity of the top 3 e of the lower portion 3 b of the outercircumference 3 of the inflator housing 2 (i.e. the top 3 e of theportion 3 b of the outer circumference 3 of the inflator housing 2disposed towards the void space 53).

With this configuration, when the inflator housing 2 is disposed at theheating position HP, the semicircular arc portion 49 of the heating coil46 disposed opposite to the void space 53 encircles the upper half outercircumferential portion 3 a of the housing 2 in proximity and thestraight portions 50 and 51 are disposed proximate to the lower sideportions 3 c and 3 d (see FIG. 3) of the outer circumference 3 thoughnot in an encircling manner, thus the coil 46 encircles a generallyentire outer circumference 3 of the housing 2 over the entire lengthexcept a portion facing the void space 53. Therefore, the heating coil46 is able to heat the housing 2 efficiently by induction heating.Needless to say, the void space 53 has an opening width greater than adiameter ID (FIG. 3) of the housing 2 and is disposed at a position inthe direction YD perpendicular to the axial direction XD of the housing2 as set at the heating position HP, thereby facilitating setting andejection of the inflator housing 2 in and out of the heating position HPby the heating coil 46.

In the pressure test device 20 of the illustrated embodiment, the voidspace 53 is disposed at a lower portion of the heating coil 46 such thatthe heating coil 46 receives the inflator housing 2 as laid horizontallyfrom below the void space 53.

With this configuration, if the inflator housing 2 as laid horizontallyis moved upward from the waiting position WP into the heating coil 46via the void space 53, the housing 2 is set at the heating position HPproximate to the coil 46. Further, since the setting of the inflatorhousing 2 at the heating position HP can be conducted merely by movingthe housing 2 upward, the holding member 26 may be composed of such amember as the holding sections 27 (27A, 27B) of the foregoing embodimentthat merely supports the underside of the housing 2, i.e. the holdingmember does not have to be composed of a chucking mechanism or the likethat grips the housing 2. Each of the holding sections 27 of theforegoing embodiment includes, on the top plane 28, a V-shaped holdingrecess 29 that accommodates the housing 2 and prevents the housing 2from slipping or rotating. Although a chucking mechanism or the likewould be likely to be formed of metal material including a spring or thelike, such a holding member as the holding member 26 of the foregoingembodiment may be fabricated of non-conducting material like syntheticresin. That way the pressure test device 20 will have only to heat theinflator housing 2 but not the holding member 26, and heating of theinflator housing 2 will be conducted further efficiently.

What is claimed is:
 1. A pressure test device for testing a heatresistance of an inflator housing, comprising: a heating apparatus thatheats the inflator housing which is made from metal into a generallycylindrical contour and is filled with a gas, the heating apparatusincluding: a conducting wire; a heating coil that is connected with theconducting wire and causes induction heating in the inflator housing asset at a heating position; and a power supply that feeds ahigh-frequency electric current to the conducting wire.
 2. The pressuretest device of claim 1, wherein the heating coil is disposed at aposition in a direction perpendicular to an axial direction of theinflator housing as set at the heating position.
 3. The pressure testdevice of claim 2, wherein: the heating coil includes a void space thatserves as an insert/eject port of the inflator housing into and out ofthe heating position; and the heating coil is configured to cover aportion of an outer circumference of the inflator housing opposed to thevoid space over a generally entire length.
 4. The pressure test deviceof claim 3, wherein the heating coil is formed into such a bent plateshaped generally like a half-pipe that is adapted to encircle theportion of the outer circumference of the inflator housing opposed tothe void space.
 5. The pressure test device of claim 4, wherein: aprojected contour of the heating coil as viewed from the axial directionof the inflator housing as set at the heating position is such a U shapethat includes a semicircular arc portion which is opposed to the voidspace and covers a generally half circumference of the inflator housingand a pair of straight portions that extend straightly in parallel toeach other from both ends of the semicircular arc portion; and at leastleading ends of the straight portions extend to a vicinity of a top of aportion of the outer circumference of the inflator housing disposedtowards the void space.
 6. The pressure test device of claim 3, whereinthe void space is disposed at a lower portion of the heating coil suchthat the heating coil receives the inflator housing as laid horizontallyfrom below the void space.